This invention relates to a method of joining dissimilar metals through a combination of mechanical interlocking, diffusion bonding, and shrink fitting. The present invention is particularly suited for joining incompatible metals without the formation of excessive brittle intermetallic phases, and will be described with particular reference to the joining of a titanium matrix composite to a nickel-base super-alloy.
Many methods are known for joining dissimilar metals without the use of mechanical fasteners or conventional welding techniques. These methods include diffusion bonding, shrink fitting, and mechanical attachment among others. These processes used by themselves, are not completely satisfactory because they fail to produce a joint that can withstand rotational forces as well as tension and compression. Diffusion bonding utilizes the application of heat and pressure to physically merge the joining metals. In diffusion bonding, certain metals, such as, for example, nickel-based INCONEL 718 and titanium-based TI-6AL-4V, the technique, because of the high temperatures required creates certain undesirable intermetallic phases in the areas adjacent to the interface between the metals. Shrink fitting as a method of joining different metals utilizes the differential thermal expansion during cooling to produce a joint. The strength of the joint produced by each process is low and the use of the method is limited because it can be used only with certain geometries. Mechanical attachment is generally inefficient and does not provide a fully rigid joint.
There has been a need to provide an effective method for joining metals of the foregoing type while eliminating those problems typically associated with prior known joining methods and techniques. The subject invention is deemed to meet these needs, to overcome the above-expressed problems and others, and to provide a process for joining dissimilar metals which are normally incompatible for direct metallurgical union.